This invention relates generally to sleeping bags, and more specifically to a sleeping bag that is selectively convertible between a compact foot space configuration and an expanded foot space configuration.
Consumers face a difficult task in finding a sleeping bag that meets their needs over a wide variety of ambient temperatures in which the bag is intended to be used. Mummy-type sleeping bags are well suited for use in outdoor, cold ambient temperatures. Mummy bags generally minimize internal volume, being shaped with a lateral taper to approximately contour the body of a person. These bags are effective in conserving heat by decreasing air movement within the bag. A drawback to mummy bags is that some people feel discomfort in the relatively snug space of these bags. Their freedom of motion is reduced, especially at their feet, and they are too warm when the bag is used in warmer ambient temperatures. Rectangular-type sleeping bags are well suited for use indoors or in milder outdoor temperatures. These bags are shaped with a generally constant lateral dimension, providing generally good knee and foot room and freedom of motion. Although rectangular bags are generally more spacious than mummy bags, a drawback is that their larger internal volumes make them thermally inefficient. When used in colder environments, persons using rectangular bags can more easily become chilled, especially toward their feet.
Unfortunately, sleeping bag designs typically incorporate a one-type-fits-all approach, having volume and taper that are fixed. People who want to use bags in both colder and milder temperature environments must either purchase two bags (i.e., a mummy bag and a rectangular bag) at considerable expense, or get by with one bag designed for one environment but which is less than ideal in the other environment. Some users may have a personal preference for a snugger, warmer bag regardless of foot space. Other users prefer a roomier bag, regardless of its thermal characteristics. Unfortunately, no single type of sleeping bag is available that will please both.